1) Field of the Invention
The invention is in the field of Microelectromechanical Systems (MEMS).
2) Description of Related Art
A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. Crystal oscillators, such as quartz oscillators, are commonly used to generate frequencies to keep track of time (as in quartz clocks) or to provide a stable clock signal for digital integrated circuits. Usually, a different crystal is required for each desired frequency. Also, the crystal and the oscillator circuit components are typically distinct from one another, i.e. they are not integrated.
For the past several years, MEMS structures have been playing an increasingly important role in consumer products. For example, MEMS devices, such as sensors, detectors and mirrors, can be found in products ranging from air-bag triggers in vehicles to displays in the visual arts industry. In another example, high quality MEMS oscillators may be used in place of crystal oscillators to keep track of time and to provide a stable clock signal for digital integrated circuits. As these technologies mature, the demands on precision and functionality of the MEMS structures have escalated. For example, optimal performance may depend on the ability to fine-tune the characteristics of various components of these MEMS structures. Furthermore, consistency requirements for the performance of MEMS devices (both intra-device and device-to-device) often dictate that the processes used to fabricate such MEMS devices need to be extremely sophisticated.
Certain applications may require the generation of multiple frequencies. Crystal oscillators exhibit low phase noise and high precision, but a separate crystal is required for each desired frequency. This approach may not be compatible with highly compact spatial requirements often associated with current electronics applications. Space constraints may be addressed by using MEMS oscillators which may be fabricated on the same substrate as the corresponding MEMS oscillator circuits, i.e. as part of an integrated circuit, with multiple oscillators fitting on a single substrate. However, the quality of the frequency generated by a MEMS oscillator may not be as high as that of a crystal oscillator.
Thus, a hybrid system having a non-MEMS device and a MEMS device is described herein.